Motor vehicle applications subject battery systems to harsh mechanical conditions. Mechanical stresses are caused by widely varying temperatures caused by ambient temperature fluctuations and varying internal heat generation. In addition, vehicles can subject battery systems to continuous and long-term vibrations that degrade efficiency. In addition, performance and reliability demands are extremely high while cost and mechanical constraints are generally very tight. For example, demanding applications for vehicle battery systems, such as hybrid and electric vehicles, require long life, high power output, as well as temperature and vibration tolerance. In light of these design constraints, it is often difficult to design mechanical packaging systems that function reliably.
It is believed that existing battery system designs do not minimize or address numerous points of failure. Large battery storage systems, such as used in electric vehicles and hybrid vehicles, generally include many separate battery cells to store sufficient power. In some systems, it is convenient to assemble the cells into packs of many cells that are then combined in a suitable number into a battery module that provides the total capacity for the system. It is believed, however, that many interconnections are required to assemble the cells and that each interconnection provides a failure point in the system.
The charging and discharging of battery storage systems is generally managed to maximize the life spans of all the cells. Proper power management is aided by a battery management controller which measures the voltages of the battery cells or groups of cells. Voltage measurement of many cells presents problems in terms of accuracy and the practical interconnections between the cells and the controller. For example, connections used to measure voltage can imbalance the discharge rates of cells and adversely affect the voltage measurements provided. Problems also arise when cells are interconnected in series, which poses a risk of overcharging. Overcharging can negatively affect the cell lifespan.